This invention generally relates to methods for determining the position of moveable internal components such as a crankshaft, in an internal combustion engine, and deals more particularly with a method for determining the stopping position of the crankshaft relative to the timing cycle of the engine""s cylinders (hereafter referred to as xe2x80x9cengine stopping positionxe2x80x9d).
In order to control ignition timing, fuel injection and other functions in an internal combustion engine, it is necessary to determine the angular displacement of the engine""s crankshaft with each stroke. In many cases, it is also necessary to determine the angular position of the engine""s camshaft, particularly where variable cam timing systems are employed to vary the timing between a camshaft and the crankshaft. In order to achieve smooth engine startup without misfires following engine shutdown, it is necessary to know the final angular position of the crankshaft relative to the engine""s firing sequence and cylinder cycle timing. When the ignition is shut off and the engine comes to a stop, the measured final crankshaft position and final cycle state (e.g. compression stroke) of the engine""s cylinders is stored in the memory of a power train control module or similar controller, which then uses this information during engine startup to synchronize the fuel injection with the engine cylinder cycle timing.
In order to accurately synchronize the fuel injection for the needed start, it is necessary to determine the rotational position of the engine. Camshaft position information is needed in order to know which part of the four stroke cycle the engine is on. Sensors typically used to sense camshaft angle position such as variable reluctance sensors do not provide accurate information at low engine speed, e.g. speed below 250 crank RPM""s. Consequently, ambiguity may exist in the information that is recorded to indicate the final stopping position of the engine. Attempts have been made to resolve such ambiguities through estimates based on sensor data but these techniques do not assure that the recorded engine stopping position data is accurate.
Accordingly, there exists a need for a method of determining the stopping position of an engine which can detect the engine""s final stopping position consistently and accurately. There also exists a need to associate the data indicating the final stopping position of the engine with information indicating which part of a four stroke cycle the engine is on, using conventional sensors for determining the rotational positions of the camshaft and crankshaft.
It is an object of the present invention to provide a method for accurately determining the final stopping position of an internal combustion engine by interpreting information contained in a periodically varying crankshaft position signal whose amplitude and frequency vary as a function of the speed and rotational position of the crankshaft.
In accordance with the primary object of the invention, in a preferred embodiment, the method comprises generating a periodic crankshaft position signal having an amplitude and frequency that vary as a function of the speed and rotational position of said crankshaft; for each half period of said signal, obtaining the ratio of the amplitude of said signal to the time interval of the corresponding half period; generating a set of secondary ratios to obtain a set of ratio values; successively comparing the calculated ratio values with a preselected constant value, the results of the comparisons indicating slow down and continued rotation in the same direction or stoppage and reversal of the rotational direction of said crankshaft; and, updating a record indicating the current rotational position of said crankshaft based on the results of the comparison.
An advantage of the present method is that by using position information generated by conventional sensors and performing calculations involving the position data, a record can be generated of the engine position which can distinguish between the engine slowing down and continuing on in the same direction or slowing down and reversing rotational direction. An added advantage of the invention is that the method may be employed with crankshaft position sensors that rely on a missing tooth on a crankshaft sprocket commonly employed as a reference mark for determining angular crankshaft position.